A directionally tunable but frequency-invariant beamformer on an acoustic velocity-sensor triad to enhance speech perception

Herein investigated are computationally simple microphone-array beamformers that are independent of the frequency-spectra of all signals, all interference, and all noises. These beamformers allow the listener to tune the desired azimuth-elevation “look direction.” No prior information is needed of the interference. These beamformers deploy a physically compact triad of three collocated but orthogonally oriented velocity sensors. These proposed schemes’ efficacy is verified by a jury test, using simulated data constructed with Mandarin Chinese (a.k.a. Putonghua) speech samples. For example, a desired speech signal, originally at a very adverse signal-to-interference-and-noise power ratio (SINR) of -30 dB, may be processed to become fully intelligible to the jury

Optimum pilot pattern for MMSE channel estimation in single-carrier MIMO systems

The minimum mean squared error (MMSE) channel estimator (CE) can provide receiver performance better than the least square (LS) CE. However, the MMSE CE usually uses a pilot pattern optimally designed for the LS CE. In this paper, we derive an optimum pilot pattern for the MMSE CE in single-carrier MIMO systems assuming that both the transmitter and receiver know the average channel information, such as the channel correlation matrix and signal to interference and noise power ratio. Analytic and simulation results show that the MMSE CE with the use of the proposed pilot pattern can reduce the MSE compared to the use of one optimized for the LS CEThis work was supported (in part) by the Ministry of Information & Communications, Korea, under the Information Technology Research Center (ITRC) Support Program

Mixed numerologies interference analysis and inter-numerology interference cancellation for windowed OFDM systems

Extremely diverse service requirements are one of the critical challenges for the upcoming fifth-generation (5G) radio access technologies. As a solution, mixed numerologies transmission is proposed as a new radio air interface by assigning different numerologies to different subbands. However, coexistence of multiple numerologies induces the inter-numerology interference (INI), which deteriorates the system performance. In this paper, a theoretical model for INI is established for windowed orthogonal frequency division multiplexing (W-OFDM) systems. The analytical expression of the INI power is derived as a function of the channel frequency response of interfering subcarrier, the spectral distance separating the aggressor and the victim subcarrier, and the overlapping windows generated by the interferer's transmitter windows and the victim's receiver window. Based on the derived INI power expression, a novel INI cancellation scheme is proposed by dividing the INI into a dominant deterministic part and an equivalent noise part. A soft-output ordered successive interference cancellation (OSIC) algorithm is proposed to cancel the dominant interference, and the residual interference power is utilized as effective noise variance for the calculation of log-likelihood ratios (LLRs) for bits. Numerical analysis shows that the INI theoretical model matches the simulated results, and the proposed interference cancellation algorithm effectively mitigates the INI and outperforms the state-of-the-art W-OFDM receiver algorithms

Fast cell site selection with interference avoidance in cellular packet based OFDM systems.

In this paper, we consider fast cell site selection (FCS) in packet based OFDM cellular systems. Mobile station (MS) in multi-coverage regions or soft handover region can have opportunities to select a link better than from the current cell. Conventional FCS schemes track the channel fading variation, achieving a selection diversity gain [1]. However, MSs near the cell boundary suffer from other cell interference (OCI) which is highly time-varying and unpredictable. Therefore, it may be desirable for FCS to reduce the OCI effect near the cell boundary. In this paper, we propose an FCS scheme with interference avoidance for a packet based OFDM system and analyze its performance. Finally, the analytic performance of the proposed scheme is verified by computer simulatio

Effect of channel estimation error on packet-based multi-user OFDM systems

In this paper, we consider the performance of a packetbased multi-user orthogonal frequency division multiplexing (OFDM) wireless system in the presence of channel estimation error. To investigate the effect of incorrect channel information on the system performance, we consider the use of two channel estimation schemes; one is a simple linear and the other is an optimum Wiener-type channel estimator. We analyze the effect of channel impulse response (CIR) estimation error on coherent reception and the effect of instantaneous signal to interference and noise ratio (SINR) estimation error on channel aware techniques associated with packet scheduling. It is shown that the performance of coherent reception is relatively less susceptible to the CIR error, but the performance of channel aware schemes can be very sensitive to the SINR estimation error, mainly due to incorrect scheduling. To alleviate this scheduling problem, we propose an improved scheduling method which can be employed even with the use of a simple channel estimator. Finally, we verify the performance of the proposed scheduling scheme by computer simulation

A Pre-FFT OFDM adaptive antenna array with eigenvector combining

Abstract-This paper proposes a novel pre-FFT type OFDM adaptive array antenna called "Eigenvector Combining." The eigenvector combining is a realization of a post-FFT type OFDM adaptive array antenna through a pre-FFT signal processing, so it can achieve excellent performance with less computational complexity and shorter training symbols. Numerical results demonstrate that the proposed eigenvector combining shows excellent bit error rate performance close to the lower bound just with two training symbols. I. INTRODUCTION Orthogonal frequency division multiplexing (OFDM), which is a pre-distortion or an equalization technique at transmit side in a sense, is an efficient technique for high-speed digital transmission over severe multipath fading channels To maintain high-speed reliable wireless communications systems, the use of multiple antennas at receive side has been considered as an effective tool not only for gain enhancement, increased spectral efficiency[3] but also for interference suppressio

Packet scheduling in the presence of channel estimation error in multi-user OFDM wireless systems

In this paper, we investigate the effect of channel estimation error on the performance of channel aware techniques in a packet-based multi-user OFDM wireless system. To this end, we consider the use of two channel estimation schemes; one is a simple linear and the other is an optimum Wiener-type channel estimator. We examine the effect of channel impulse response (CIR) estimation error on coherent reception and the effect of signal-to-interference and noise ratio (SINR) estimation error on channel aware transmission techniques (e.g., packet scheduling). It is shown that the performance of coherent reception is relatively less susceptible to the CIR estimation error, but the performance of channel aware schemes can be very sensitive to the SINR estimation error. To alleviate this problem, we propose a robust scheduling scheme which can work without significant performance degradation even in the presence of large channel estimation error. Finally, we verify the performance of the proposed scheduling scheme by computer simulation.Ministry of Information & Communications, Kore

Design of pilot signal for MC-CDMA uplink systems

Coherent demodulation needs to maintain the symbol timing synchronization and to estimate the channel response in multicarrier code division multiple access systems. The use of inverse DFT (IDFT) is often considered to generate a pilot signal for this propose. However it requires a large implementation complexity, making it impractical for real applications. In this paper, we consider the design of a novel pilot signal for both symbol synchronization and channel estimation. By controlling the design parameters, the pilot signal can be generated to provide a desired signal-tointerference noise power ratio, while maintaining an acceptable peak-to-average power ratio. Simulation results show that the use of the proposed pilot signal can improve the detection performance compared to the use of conventional IDFT-based pilot signal, while significantly reducing the implementation complexity

Adjacent Channel Interference Aware Joint Scheduling and Power Control for V2V Broadcast Communication

IEEE This paper proposes scheduling and power control schemes to mitigate the impact of both co-channel interference (CCI) and adjacent channel interference (ACI) on direct vehicle-to-vehicle broadcast communication. The objective is to maximize the number of vehicles that can communicate with the prescribed requirement on latency and reliability. The joint scheduling and power control problem is formulated as a mixed Boolean linear programming (MBLP) problem. A column generation method is proposed to reduce the computational complexity of the joint problem. From the joint problem, we formulate a scheduling-alone problem (given a power allocation) as a Boolean linear programming (BLP) problem and a power control-alone problem (given a schedule) as an MBLP problem. The scheduling problem is numerically sensitive due to the high dynamic range of channel values and adjacent channel interference ratio (ACIR) values. Therefore, a novel sensitivity reduction technique, which can compute a numerically stable optimal solution at the price of increased computational complexity, is proposed. Numerical results show that ACI, just as CCI, is a serious problem in direct vehicle-to-vehicle (V2V) communication due to near-far situations and hence should not be ignored, and its impact can be reduced by proper scheduling and power control

An Error Rate Comparison of Power Domain Non-orthogonal Multiple Access and Sparse Code Multiple Access

Non-orthogonal Multiple Access (NOMA) has been envisioned as one of the key enabling techniques to fulfill the requirements of future wireless networks. The primary benefit of NOMA is higher spectrum efficiency compared to Orthogonal Multiple Access (OMA). This paper presents an error rate comparison of two distinct NOMA schemes, i.e., power domain NOMA (PD-NOMA) and Sparse Code Multiple Access (SCMA). In a typical PD-NOMA system, successive interference cancellation (SIC) is utilized at the receiver, which however may lead to error propagation. In comparison, message passing decoding is employed in SCMA. To attain the best error rate performance of PD-NOMA, we optimize the power allocation with the aid of pairwise error probability and then carry out the decoding using generalized sphere decoder (GSD). Our extensive simulation results show that SCMA system with “5×10” setting (i.e., ten users communicate over five subcarriers, each active over two subcarriers) achieves better uncoded BER and coded BER performance than both typical “1×2” and “2×4” PD-NOMA systems in uplink Rayleigh fading channel. Finally, the impacts of channel estimation error on SCMA , SIC and GSD based PD-NOMA and the complexity of multiuser detection schemes are also discussed